Magnetic bubble memories are now well known in the art. One mode of moving bubbles in a layer of bubble material employs a pattern of magnetic elements in a plane closely spaced with respect to and coupled to the layer of bubble material. The elements, in a most familiar form comprise a magnetically soft material, such as permalloy, but may also comprise ion implanted regions or grooves, etc. Successive portions of the elements become temporarily magnetized in response to a magnetic field rotating in the plane of the bubble layer in a manner to move bubbles along paths defined by the elements as is now well understood.
Frequently, the magnetic elements are organized to define closed loop paths for recirculating bubble patterns. In such closed loop paths, bubbles move clockwise or counterclockwise depending on the geometry of the elements and/or the direction of rotation of the field. In any case, bubbles move in one direction in one leg of the loop and in opposite direction in the other. To realize bubble movement of this type, elements in one leg are arranged symmetrically with respect to the elements in the other. Adjacent elements in a leg are spaced apart four bubble diameters, the legs being similarly spaced apart four diameters to avoid interaction between bubbles.
Bubble memories in which bubbles are moved by temporarily magnetized elements are usually organized in a manner where a plurality of closed loops recirculate bubbles through positions where transfer of information occurs on a controllable basis between the loops and an accessing channel. The requisite minimum separation of the legs of a loop determines a maximum packing density for a bubble layer of a specified size. Accordingly, a pattern of elements which permits the legs of a recirculating loop to be relatively closely spaced also permits an increased packing density.